[Steve L]

Greetings all. I recently started using a 7.5 gallon kettle with a false bottom as a mash tun so I can use direct fire to maintain temps. I insulated if with multiple layers of reflectix and I recirculate with a mark II pump from the ball valve back on top of the mash. He first time I used this method, my efficiency dropped by about 20 percent fro. What I bet with my cooler, to about 55 percent. Not sure what I'm doing wrong or if this is to be expected. I was recirculating for the entire mash at about 1 gallon per minute and just had my outlet hose laying on top of the mash with no form of manifold. Any help or suggestions is greatly needed.
Thanks

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[stpug]

It should not affect efficiency to any great degree.  Generally speaking, folks see improvement in efficiency not the other way around.  My guess - total guess - is that your recirculation was channeling and your lautering also pulled from those channels, missing a bulk of sugars within the non-channelized portion of the grist.

[Stevie]

Yeah, channeling would be my first guess. Try scoring the top of be grain bed after it is set.

[theDarkSide]

I think the directions for the Blichmann Brew Easy say to stir the top 1/3 of the mash 15 minutes in (and maybe every 15 minutes...not sure about that one) so maybe this would help.

I use a grainfather so there's a top plate that disperses the recirculation evenly onto the grain bed.

[brewinhard]

And stick that return tubing under the surface of the mash to minimize oxygen pickup.

[ynotbrusum]

I had the same problem, but the Locline sparge halo solved the issues for me:

https://www.brewhardware.com/product_p/mashspargering.htm

Any similar sparge device should bring better results.  Also consider a gentle stir every 15 minutes or so during the mash, if you don't mind the haziness it creates...not a problem as far as I am concerned, other than the O2 pickup (if you are trying Low O2 processes).

[mabrungard]

I find that recirculation increases efficiency. I'm betting that your runoff duration may have been too short. Since you had recirculated the wort, that action improves the permeability of the grain bed and if you are used to running off at whatever rate the bed will flow at, it could easily have drained too fast.

PS: I'm not too fond of the recommendation to cut the top of a grain bed to reduce short-circuiting or improving mash flow. My 30 yrs experience as a geotechnical engineer and flow through granular media suggest a better option. A more typical occurrence with recirculating flow is that a mucky layer (schmutzdecke) forms on top of the grain bed. That impedes flow through the bed and can cause flow to short-circuit along the walls of the tun. To reduce the schmutzdecke, it is better to mix that stuff into the upper couple of inches of the grain bed to break it up and prevent its reforming. Mix the entire top of the bed.   

[Steve L]

Great, thank for all the info. I did notice that when I drained the may tun, there as a distinct "washout" kind of cavity where my output tube had been sitting along the back edge of the tun. Definitely possible it may be a channeling issue. Also, when I've batch sparged in the past, I would just crank the valve on my cooler mash tun wide open and let it rip. What is the best rate at which to drain?

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